A landslide caused by erosion on the bank of the Chu River in Thieu Do commune, Thanh Hoa province. Photo by VnExpress/Le Hoang

An angry mob went on the rampage after spotting local officials on an illegal sand dredger.

Hundreds of villagers used Molotov cocktails and bricks to chase away illegal sand miners in the northern province of Thanh Hoa on Sunday.

Villagers from Thieu Do Commune turned violent when they saw four vessels docking by the Chu River at 8 p.m., dredging sand from an old mine that was supposed to have been shut down.

The crowd became even more furious when they recognized a group of commune officials on one of the vessels, including the commune’s vice chairman.

In their rage, they burned down two watchtowers constructed by authorities to prevent illegal sand dredging and destroyed a local ranger's bed and a boat.

Angry locals remained in the area until past midnight and returned the following morning to demand answers for the sand mining and why local officials had been on one of the boats.

The highway was blocked by the large crowd, who were beating drums in protest, and police were called to the scene to maintain order.

Local officials have summoned a meeting, where they said police are investigating the sand dredging activities.

“Illegal sand mining has been going on for five years. A lot of farmland has been swept away because of erosion,” said Hoang Van Thanh, a local man.

Local people claimed that hundreds of hectares of land with corn, strawberries, sugarcane and even graves have been engulfed by the river due to illegal exploitation, which they suspect is abetted by authorities.

In recent days, dozens of meters of land have been lost to erosion each night, as vessels return to the abandoned mine, they said.

Illegal sand mining has long been a serious environmental issue in Vietnam. To crack down, the government launched a campaign in May 2017 and uncovered 840 cases of illegal sand mining. Fines of over VND10 billion ($441,000) were issued and 26 vessels were confiscated during the two-month purge.